This invention relates to improving the light fastness of organic substrates and more particularly to improving the light fastness of organic compounds useful as dyestuffs.
It is commonly accepted that organic substrates such as, for example, organic dyes tend to fade upon exposure to light. Extensive studies are constantly being carried out in various technical fields such as for printing inks, textile dyeing as well as color photography, in an effort to improve the light fastness of such organic dyes.
The present invention is advantageously used to improve the light fastness of these organic substances.
In the following descriptions, the term "organic substrate" or "organic substrate material" is used to define an organic material appearing colored or colorless to the human eye under the illumination of sunlight, including not only those materials having absorption maxima in the visible spectrum, but also those absorption maxima which lie in the infrared region or in the ultraviolet region such as optical whitening agents. In other words, the organic substrate materials which are the subject of the present invention are materials having their absorption maxima at a wavelength of from 300 to 800 nm. The present invention is particularly directed to improving the light fastness of organic substrate materials occurring in photographic materials, e.g., color films, prints, etc., in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; of fluorescent whitening agents; and dyed textiles, etc.
In this specification, the term "dye" or "dyestuff" refers to an organic material which appears colored to the human eye under the illumination of sunlight. The term "light" conceptually includes electromagnetic radiation with wavelengths of from about 300 nm to about 800 nm, including ultraviolet light below 400 nm, visible light of from about 400 nm to about 700 nm and infrared rays of from about 700 to 800 nm.
It is well known that organic substrates such as, dyes or coloring agents tend to be faded by the action of light. A number of reports discussing methods of suppressing such tendency, or of improving the light fastness of such materials are known. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indoaniline, azo and azomethine dyes to visible and UV light can be improved using phenol derivatives containing condensed heterocyclic structures. As "The Theory of Photographic Process" (3rd edition-1967) authored by Mees et al explains in Chapter 17, azomethine or indoaniline dyes are generally produced in silver halide color photographic materials upon the reaction of the oxidation product of an aromatic primary amine developing agent with a color coupler. Various patents describe techniques for improving the stability to light of the dyes making up the color images. Compounds which are effective to improve the light fastness of the co-existing dye include, for example, the hydroquinone derivatives disclosed in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801, and 2,816,028 and Brit. Pat. No. 1,363,921, etc., gallic acid derivatives set forth in U.S. Pat. Nos. 3,457,079 and 3,069,262, Published Japan. Pat. Appln. 13,496/1968, etc., p-oxyphenol derivatives set forth in U.S. Pat. Nos. 2,735,765, 3,432,300, 3,698,909, 3,573,050, 3,574,627 and 3,764,337, chroman and coumarane derivatives set forth in U.S. Pat. Nos. 3,432,300, 3,574,626, 3,698,909, 3,573,050 and 4,015,990, etc. These compounds certainly are effective to prevent fading or discoloration of dye images to a certain extent but not to a satisfactory extent.
Brit. Pat. No. 1,451,000 discloses that the stability of organic substrates to light is enhanced by the use of azomethine quenching compounds which have absorption maxima at a longer wavelength than the substrate materials. Unfortunately, the fact that the azomethine quenching compound is itself colored adversely affects the color hue of the substrate material.
Metal chelates can be used to prevent degradation of polymeric materials by the action of light as is described in the following literature; J. P. Guillory & R. S. Becker, J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974), R. P. R. Ranaweera & G. Scott, J. Polym. Sci., Polym. Let. Ed., 13, 71 (1975), etc. Stabilization of dyestuffs against light by the use of metal chelates is also described in U.S. Pat. No. 4,050,938, Japanese Patent Application (OPI) 87,649/1975 and Research Disclosure 15162 (1976). However, the disclosed metal chelates exhibit an unsatisfactory fade preventing effect, and when the metal chelates are employed in a photographic emulsion, as will be established by a comparative study later, the disclosed metal chelates desensitize the silver halide probably due to an undesirable interaction with silver. Also these metal chelates exhibit an undesirably poor solubility in organic solvents, which means the working concentration of such a chelate is too low to permit a sufficient fade prevention. Moreover, these chelates cannot be present in a high concentration since they themselves are colored and therefore adversely affect the color hue and the color purity of the dyes.
Furthermore, heretofore, agents suitable for preventing the fading of cyan dyes have not been known.